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Well I've been able to raise my weekly average to around 55 mpg or so by heeding some of the advice floating around here.. And now I'm suddenly fighting for 48 this week!

It's been about 10 degrees colder and wet wet wet; it has been humid and frequently dumping down buckets of rain. I'm sensing that the water on the road is creating some drag, but is that really the main cause?

Also, I've noticed that I can't seem to get my idle stop to last more than about 10 seconds, and I'm not sure what that's about either. I've messed with my climate controls a little (lower temp, auto vs. user set), but to no avail.
 

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It takes energy to move water out of the tire path = effectively increasing rolling resistance.

Colder Air is more dense = effectively more aerodynamic drag.

Humid Air is less dense than dry air ... until you reach a certain point ... liquid water is more dense than air ... every drop of rain is that much more mass that has to be moved = more energy being spent = effectively more aerodynamic drag through this denser fluid medium.

Then there are other side effect loads ... like you are more likely to spend some additional energy on running head lights, windshield whippers, defoggers , etc.

It all adds up.

It might not account for 100% of the difference you are seeing ... but it is reasonable to expect it to contribute.
 

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Weather has a profound impact on MPG.
 

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It most certainly does. Longer warmup times, stronger winds to fight, and all the factors mentioned above. Once the weather warms up into the 60s and 70s, your mileage goes up. I've found a difference of 4 or 5 mpg between the winter and the spring. Then once it gets hot in the summer, you lose 1 or 2 mpg, if you live where you have to run the AC a lot.
 

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the more stuff you have on (a/c, lights, radio, etc.) the less auto-stop ... i believe the '10 model year also has less auto-stop designed into the car than the '11
 

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The attached is my gas mileage for my 2002 Chevy Avalanche truck (yes, lifetime MPG average 15.1994 MPG, 98,514 miles, 6,481.429 gallons, best tank MPG 19.91137, worst tank 13.02422. I have owned this vehicle since Dec 2001 and logged every tank, both manually logging the fillups, and logging the built-in trip computer. On average, I get about 2 MPG higher in the summer than the winter (roughly 15% better). I rarely use A/C, and roll the windows down when I am below 35 MPH if needed. My commute is a 17 mile one way drive, covering everything from 25 MPH residential to 55 MPH limited access roads, with about 17 stop lights and 4 stop signs. I used to go 10 to 15 over the limit (2002 - 2009) until I got a ticket in Jan 2010. Since then I have been hypermiling (2010-2011) and driving not like an old man, but like a dead man, pushing my summer highs from 16.5 to 19 MPG (15 to 20 % improvement). The car is garaged, I live near Chicago, and the garage never gets below 35 degrees. I used to take the cargo covers off of the truck bed for the summer (2002 through 2006) but keeping the tailgate shut and the covers in place appears to be worth 1 to 1.5 MPG (2007-2011). In the attached graph the temp is the red line and the MPG is the blue line.
 

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Need4Speed:
That is quite a record and an interesting graph! I noticed that as temps. go up mpg sometimes goes up and sometimes it doesn't, but that overall, temps and mpg go up and down together. I'm wondering if changes is gasoline quality ie shift or non-shift to winter gas in your area, would explain your experience?
I heard on the radio this morning that "summer gas" is going to be phased out over the next two weeks to be replaced with lower cost to produce "winter gas." The winter gas has less energy in it, ordinarily reducing my mpg 1-3 mpg (even though there is little change in weather conditions). When summer gas returns I'll often regain that lost 1-3 mpg.
 

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I have also thought that maybe the summer/winter gas blends affect the MPG but have not been able to see that from my data. In Illinois the summer blend is required between May 1 and Sept 15 (tomorrow).
 

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Also, sometimes in the earlier years I took off the bed covers for the summer. You will see the MPG start to climb in the early summer as the temp climbs, then I would remove the covers and lose one to two MPG, late in the summer I would put the covers back on and it would jump up again, before then falling with the temperatures. Once I saw the drop in MPG I started to leave them on at all times unless I had something in the bed. Also, once in a while I would have some out of the ordinary drives, maybe a tank that was mostly highway, or the one tank where I drove with a car trailer that result in abnormal jumps in the MPG. I check my tire pressure regularily (3 PSI over door sticker to prevent cupping). I have winter and summer tires and log exactly when they get swapped out, no difference with the tires.
 

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Jim - you have all of the goodies - 5 speed, mima, tail, fas, grid charger, etc. I have a cvt, wish I had mima....

Can I add a fuel cutoff to my cvt without any issues? With the cvt the only way that the injector duty cycle goes to zero is when I lift off the gas far enough to get regen. There is no way to get zero injector pulse width and not be in regen. I basically need to be coasting down hill in regen to get no fuel consumption. I know that there are a number of places that I would like to be able to coast with no fuel usage. With all the issues with cvt transmissions puking I don't want to consider shifting to neutral for engine off coasting. I have heard it is not a nice noise when going from neutral back to drive at speed. If a fuel cutoff is used, does the fcd actually know about it and compute the correct mpg?
 

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I have been at my current job now for almost 11 months, and here is the plot of mpg versus temperature. Tracks extremely well.....

This is very intersting.
When I was an independant distributer of a fuel saving product, I learned that winter gas is different in cold climates.
Petrol companies add more ethanol and buthane to their car gas during winter than during summer to improve cold strarting. But these products have less energy per volume than pure octane. Gas is a blend, not a pure standardised subtance.

When you add the air conditioning, which is actually an air cooling system, it's very costly on the HP needed from the engine. Then you lose on the mpg because your engine needs to provide about 5 HP just for the inneficient old technology A/C.

Transit
 

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Can I add a fuel cutoff to my cvt without any issues?
I have not investigated this. Sorry.

If a fuel cutoff is used, does the fcd actually know about it and compute the correct mpg?
Yes, the FCD does in fact keep track of the mileage with performing Engine-Off or Engine-On coasting.

What is more disruptive, is Key-Off - Engine-Off coasting. It works, but sometimes the display gets scrambled and you get 150mpg indicated until you key-off again.

Jim.
 
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